MEPS 540:87-98 (2015)  -  DOI: https://doi.org/10.3354/meps11513

ABSTRACT: Parasites are known to induce phenotypic modifications in their hosts through direct competition for resources, which can negatively affect host fitness. Although parasite-induced phenotypic variation has been studied extensively in terrestrial and freshwater taxa, this phenomenon remains comparatively under-studied in marine pelagic invertebrates, such as ecologically important jellyfish. Here we studied the parasite–host relationship between Edwardsiella sp. anemone larvae (parasite) and medusae of Aurelia sp. 5 (host) in an isolated marine lake (Veliko Jezero) in Croatia. During 3 different seasons, we quantified differences in the vertical position in the water column, morphology, and egg production between parasitized and unparasitized medusae. Our results revealed that medusa behavior, morphology, and fecundity can be significantly affected by parasitism. Infected medusae were more abundant higher in the water-column where water was warmer, while unparasitized individuals displayed the opposite pattern. In addition, host somatic growth, gonad size, and egg production were negatively affected by parasitism, suggesting an ultimate negative effect on medusa fecundity. Parasitized individuals, however, developed relatively longer manubria and produced larger eggs than unparasitized counterparts, indicating a compensatory response to increase capture surface and reproductive effort. This study demonstrates the extent of parasite-induced phenotypic variation in jellyfish as well as the role of parasites in potential regulation of jellyfish population size.

KEY WORDS: Parasitism · Plasticity · Jellyfish · Edwardsiella · Mljet